Unfortunately trashing the preferences didn't work. I'm using a G5 dual with over 4 gb's, and both Logic 7 and 8 are updated...getting a question mark over the L7 icon in the dock now. 7 does open for a few seconds and then either shuts down or the program remains visible with a white patch appearing without anything in it and the dreaded beach ball appearing, reminding me to force quit.
When I try to open L8 with the same session (noted that not all of my sessions are having this problem...only the the one I most need right now), it does load up, but does not respond when trying to playback...while some operations do work sometimes, like changing to different channel strips. But these actions always result in the warning of other audio or midi devices interfering.
The Logic 7 project doesn't open at all in L8. And for the record, ever since I loaded L8, I have never been able to open any sessions in L7...I guess that refers to the first question...no, Logic 7 doesn't open at all.